CAS drill guide and drill tracking system

ABSTRACT

A drill guide assembly ( 10 ) for a drilling tool ( 50 ) having a chuck engaging a bit portion ( 54 ) comprising a tip ( 62 ) and a length extending from the chuck, the drill guide assembly comprising a first member ( 14 ), a second member ( 12 ) and a trackable member ( 16 ). The first member ( 14 ) is adapted to abut a workpiece surface and defines a central aperture ( 19 ) therethrough adapted to receive the bit portion. The second member ( 12 ) is adapted to be axially displaced with respect to the first member and is axially biased therefrom, and defines a central aperture ( 11 ) therethrough adapted to receive the bit portion. The trackable member ( 16 ), fastened to the second member, comprises a detectable element ( 35 ) adapted to be located and tracked in three dimensional space, thereby defining the position and movement of the second member and therefore that of the drilling tool bit portion.

CROSS-REFERENCE TO RELATED APPLICATIONS

This application is a divisional of U.S. patent application Ser. No.10/123,237, filed on Apr. 17, 2002, the entire contents of which isincorporated herein by reference.

TECHNICAL FIELD

The present invention relates to surgical devices, and more particularlyto a drill guide adapted to provide guidance and tracking of a drillingtool when used in conjunction with a computer aided surgical system.

BACKGROUND OF THE INVENTION

Many surgical procedures, particularly those used in orthopaedicsurgery, require holes to be drilled in a bone of a patient. Surgicaldrills have long been used for this purpose, and various mechanicalguidance instruments exist to enable a surgeon to accurately drill ahole to a correct depth and without danger of damaging the surroundingtissue. Such drill guides often provide a visual depth gauge whichrequires the surgeon to read the depth of the drilled hole off agraduated scale on the instrument.

U.S. Pat. No. 5,895,389 issued Apr. 20, 1999 to Schenk et al. disclosessuch a drilling guide and measuring instrument. The guide generallycomprises a sleeve and a plunger that telescopes within the sleeve, bothhaving axial bores adapted to receive and guide a portion of a drillingtool that protrudes beyond a drill chuck. A plurality of fingers on theforward end of the plunger are biased inwardly by an inside wall of thesleeve, providing a frictional, sliding fit. Therefore the plunger andsleeve retain their relative telescopic position after they have beenpartially collapsed. Gradations on the side of the plunger indicate therelative movement of the plunger with respect to the sleeve, andtherefore the penetration depth of the drill. The sleeve preferably hasa small handle for controlling the drilling guide. An alignment boreextends through the handle in parallel with the central axis of thesleeve and plunger bores. By sliding the handle with the alignment boreover a guide wire pre-inserted into the workpiece, the drilling guidemay be aligned with the parallel wire at a predetermined distancetherefrom.

With the advent and growing use of computer aided surgery (CAS), muchgreater accuracy is possible for many surgical procedures. Surgeons cannow plot on a computer generated 3D model of the patient, before theactual procedure, the ideal location, orientation and depth of a drillhole, for example. During the surgery, position of the instruments withrespect to scanned images of the body parts can be displayed on monitorsto guide the surgeon during the procedure.

One CAS system currently employed comprises the use of at least twocameras, located at different stationary reference points, whichsimultaneously record the location of a moving three point axis. Knowingthe positions of the reference points, the unique position in space ofthe three point axis, and therefore any object to which the axis isfixed, is uniquely defined and can therefore be precisely tracked.

While such instrumentation tracking systems work well for someapplications, problems nevertheless exist with certain current surgicaluses of visually tracked systems. In order for the cameras to recordaccurate simultaneous images of the three point tracker axis, and forthe location of the points of the axis to be correspondingly preciselycomputed, the visual images of the axis must remain relativelydistortion free. As such, any displacement of the tracker axis withrespect to the surgical tool to which it is fastened, results ininaccurate calculation of the exact three dimensional (3D) spatialposition, and therefore inaccurate representation on the computermonitors of the operative instrument with respect to the patient.Therefore, the attachment brackets and fixation adapters for securelylocating the tracker axis to the tool are often complex.

CAS systems have been employed in conjunction with a surgical drill toattempt to monitor the location and depth of holes drilled into the boneof a patient for such surgical procedures as pin implantation andprosthesis fixation. For such applications, CAS three point tracker axishave been fastened directly to the drill.

A major problem associated with current attachment methods for fixing aCAS tracker axis to a drilling tool, is that many hospitals usesignificantly different drill systems. Therefore fastening a CAS trackeraxis to each type of drill requires many parts and a completelydifferent set of complex fixation adapters in every case. Thisnecessitates a custom installation for fixing a CAS tracker axis to eachand every type of surgical drill, thereby adding considerable expense toCAS systems which already represent a significant expenditure forhospitals. Additionally, the added bracketry required to sufficientlyfix the CAS tracker axis to the drill, causes an unnecessary reductionin the freedom of movement that the surgeon has to manipulate the drill.

Therefore, accurate real time visual or electromagnetic tracking ofinstruments used to drill holes during surgeries has been so far beenimpractical and expensive for widespread use with all types of surgicaldrilling systems.

SUMMARY OF THE INVENTION

A need exists to provide an improved universal drilling instrument foruse with all types of surgical drill systems such that a CAS system canproduce an accurate visual representation of the drill bit with respectto the workpiece, and therefore ensures the surgeon can accuratelydetermine the hole location, depth and orientation created using anytype of drilling tool system.

It is an object of the present invention to provide a universalinstrument which allows CAS drill tracking.

It is another object of the present invention to provide an improvedsurgical drill guide.

It is a further object of the present invention to provide a surgicaldrill guide that includes a CAS tracking axis.

It is a further object of the present invention to provide a CAS trackedsurgical drill guide that is easy to use.

It is a further object of the present invention to provide a surgicaldrill guide capable of providing improved drilling accuracy.

It is a further object of the present invention to provide a surgicaldrill guide capable of providing improved drilling precision.

It is a further object of the present invention to provide a surgicaldrill guide able to precisely indicate hole depth.

Therefore, in accordance with the present invention, there is provided adrill guide assembly for a drilling tool having a chuck engaging a bitportion comprising a tip and a length extending from the chuck, saiddrill guide assembly comprising: a first member adapted to abut aworkpiece surface and defining a central aperture therethrough adaptedto receive the bit portion of the drilling tool; a second member adaptedbe axially displaced with respect to said first member and being axiallybiased therefrom, and defining a central aperture therethrough adaptedto receive the bit portion of the drilling tool; and a trackable member,fastened to said second member and comprising a detectable elementadapted to be located and tracked in three dimensional space, therebydefining position and movement of said second member and therefore thatof the bit portion of the drilling tool.

In accordance with the present invention there is also provided adrilling system comprising a drill and a drill guide assembly, the drillhaving a chuck engaging a bit portion having a tip and extending fromthe chuck a predetermined length, said drill guide assembly comprising:a guide member defining a central aperture therethrough adapted toreceive the bit portion of the drilling tool; a collar member defining acentral aperture therethrough dimensioned to intimately receive saidguide member; said collar member and said guide member being axiallybiased, and adapted to telescope with respect to one another; one ofsaid guide member and said collar member being adapted to abut aworkpiece surface, the other of said guide member and said collar memberbeing adapted to be axially displaced with respect to said one of saidguide member and said collar member; and a trackable member, fastened tosaid other of said guide member and said collar member, havingdetectable element adapted to be located and tracked in threedimensional space, said detectable element defining the position andmovement of said other of said guide member and said collar member, andtherefore defining the position and movement of the bit portion of thedrilling tool.

There is additionally provided, in accordance with the presentinvention, a method for defining the position and movement of a drillhaving a bit portion engaged in a chuck, said method comprising:providing a drill guide adapted to receive the bit portion of the drill;fixing a trackable member comprising detectable element to a mobileportion of said drill guide, said detectable element defining a uniqueposition and orientation in three dimensional space of said trackablemember and therefore said drill guide; inserting the bit portion of thedrill into said drill guide; positioning the bit portion over aworkpiece surface and engaging said workpiece surface with a proximalend of one of the bit portion and said drill guide; and locating aposition and tracking movement of said trackable member fixed to saiddrill guide, and thereby locating the position and tracking the movementof the bit portion.

BRIEF DESCRIPTION OF THE DRAWINGS

Further features and advantages of the present invention will becomeapparent from the following detailed description, taken in combinationwith the appended drawings, in which:

FIG. 1 a is a top view of the CAS drill guide assembly of the presentinvention.

FIG. 1 b is a longitudinal sectional view taken along line 1 b-1 b ofthe CAS drill guide assembly of FIG. 1 a.

FIG. 2 is a perspective side view of the CAS drill guide assembly of thepresent invention.

FIG. 3 a is a side elevation view of the collar member of the CAS drillguide.

FIG. 3 b is an end view of the collar member shown in FIG. 3 a.

FIG. 3 c is a longitudinal sectional view of the collar member shown inFIG. 3 a.

FIG. 4 a is a side elevation view of the guide member of the drill guideof the present invention.

FIG. 4 b is an end elevation view of the guide member shown in FIG. 4 a.

FIG. 4 c is a side elevation view of the drill bit of the drilling toolto be used with the drill guide of the present invention.

FIG. 5 a is a side elevation view of the CAS trackable member of thedrill guide.

FIG. 5 b is a front elevation view of the CAS trackable member shown inFIG. 5 a.

DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENT

The computer aided surgery (CAS) drill guide assembly 10 generallycomprises a collar member 12, a guide member 14, and a trackable member16. The guide member 14 is adapted to telescope longitudinally withinthe sleeve collar member 12.

Referring generally to the assembly shown in FIGS. 1 a, 1 b and 2, theguide member 14 abuts the workpiece at a proximal end having teeth 17adapted to frictionally engaged the bone of the patient or otherworkpiece surface. A chuck portion 52 of a drilling tool 50 retains adrill bit 54 having a distal protrusion 56 which abuts end cap 26 of thecollar member 12. Spring 20 generally provides resistance, such thatcollar member 12 is biased from the guide member 14. The collar member12 generally defines an inner bore 11, and comprises an outercylindrical surface 13. A circular flange 38 radially projecting fromthe outer surface 13 of the collar member 12, provides a reaction pointfor the spring 20. The end cap 26 fits over the open end of the collarmember 12 and defines a central circular aperture 27 therein forreceiving the drill bit 54. The shaft 58 of the drill bit 54 shown infurther detail in FIG. 4 c, is adapted to extend through the inner boresin both the collar member 12 and the guide member 14, such that the tip62 of the drill bit's cutting front 60 is preferably near the proximalend 17 of the guide member 14.

The CAS drill guide of the present invention is preferably intended tobe used in conjunction with an optical tracking system which uses anetwork of cameras to locate the markers 32, so that their position andmovement can be tracked during the surgery. Pre-operative computedtomography (CT) scans of the patient create a three dimensionalanatomical model which is displayed on monitors during surgery andprovides the surgeon with an accurate representation of the specificbody parts or targeted elements of the patient. Scanned images from amagnetic resonance imaging (MRI) system can also be used to create the3-D virtual models of the patient. At the beginning of the surgery, ananatomical registration is performed which matches the patient anatomywith the 3-D digitized model displayed on the monitor, such that theposition of the tool can be shown graphically in real time with respectto the displayed model of the patient.

The length of the drill bit is preferably chosen such that when thedrill chuck is pressed against the end cap 26 of the drill guide, thedrill bit extends therethrough such that it just reaches the workpiecesurface. A shorter drill bit can be also accommodated, howeverdetermination of the zero point, or the tracker position when the tip ofthe drill bit just touches the workpiece surface, must be known toaccurately determine the depth of the subsequently drilled hole. Byrapidly moving the mobile portion of the drill guide, onto which thetrackable member is engaged, toward the workpiece, the zero point isfound when the tip of the bit portion of the drill makes contact withthe workpiece surface. The position of the trackable member, which willbe described in further detail below, when it comes to a sudden stopdefines the zero position. Therefore, the CAS system can use this pointas a reference from which to calculate hole depth, whereby any furthermovement of the drill towards the workpiece surface will be registeredby the CAS system as creating a hole in the workpiece. This also enablesthe drill bit tip position to be registered by the CAS system, such thatthe drill bit can be displayed on the CAS monitors in relation to thethree-dimensional digitized model of the patient's bone. The length ofthe drill bit used could also be pre-selected by the surgeon or CASsystem operator from among a list of drill bit types in the CASsoftware, such that once the drill guide is registered, the position ofthe drill bit tip with respect to the drill guide is known and can bedisplayed on the CAS monitors in relation to the bone model.

The depth of hole drilled into the workpiece is calculated by the CASsystem, and can be visually displayed on CAS system monitors. Thisprovides the surgeon with a precise, real time indication of the holedepth. This CAS calculated depth can be cross-checked with the physicalvisual depth sight on the drill guide, as described below, to ensurethat the hole depth is accurately displayed on the monitor. The CASsystem first prompts for a hole insertion point location to be selectedon the outer surface of the digitized 3-D model, using a mouse, footpedal, or other similar selection device. The distance measured betweenthe tip of the drill bit and the chosen insertion point, can then becalculated, and indicates the depth into the workpiece that the drillbit tip has travelled.

The hole depth calculated by the CAS system can also be used by the CASsoftware to help select the appropriate sized screw to be used. The holedepth calculation algorithm can be linked to a database of screws orother fixations for the implant system to be used, such that the mostappropriate type and size of screw can be selected and recommended tothe surgeon, based on the size and depth of hole created. Therecommended screw can be displayed as a 3-D visual representation or intext format indicating the most probable screw length.

A slot 36 in the collar member provides a visual depth sight, such thatwhen the collar member slides over the guide member, telescopically orotherwise, the position of a distal end of the guide member 14 can beseen through the sight gauge slot 36. Therefore the depth of the holecreated by the drill bit in the workpiece, which directly corresponds tothe distance travelled by the collar on the guide when using a drill bitof the preferable length as described above, can be read directly fromthe gradations 34 on the exterior surface 13 of the collar member 12.This gives the surgeon a visual verification of hole depth, and can bealso used to double check or calibrate the monitor displayed CAScalculated results.

Two opposing but offset holes 40 perforate a side wall of the collarmember 12 near the proximal end. These serve as cleaning holes, andpermit water or other cleaning fluid to be injected inside the collar toensure that any debris can be easily washed out. This inhibits possiblebuild-ups of debris which might prevent the collar member from smoothlysliding on the guide member.

The trackable member 16 generally comprises a support rod 28, and atracker head 30 having arm portions 31 extending generally radially andwhich include detectable element mounting posts 32 at the end of eacharm 31. To each mounting post 32 is removably fixed an opticallydetectable sphere 35. The detectable spheres are coated with aretro-reflective layer in order to be detected by, for example, aninfrared sensor using axial illumination. Cameras of the CAS system cantherefore detect the position of each optically detectable sphere 35illuminated by infrared. Each detectable element 35 can equally be anyother type of position indicator such as a light emitting diode ordetectable electromagnetic indicator, provided each can be detected bythe type of sensor used by the CAS system.

The support rod 28 is fixed to the collar member 12 at the end cap 26,such that all movements of the collar member, and therefore the drilland drill bit, are duplicated by the trackable member 16.

The drill guide member 14 has a circumferential radially extending endflange 15 adapted to be intimately received in the inner bore 11 of thecollar member 12. The end flange 15 of the guide member abuts theinterior stop 42, located within the collar member 12, when the springis fully extended. The guide member has a central bore 19 dimensioned toreceive the drill bit of the drilling tool. A clamp 24, providing asecond reaction point for the spring 20, is fastened to the exteriorsurface of the guide member 14 near the proximal end, at a point whichprovides a sufficient pre-load force on the spring. The clamp comprisesan external, axially projecting, member 25. This provides an attachmentpoint for a CAS instrument calibration tool, if required by the CASsystem used.

A generally radially extending handle member 18 is fixed to the clamp 24to provide the surgeon with greater control over the orientation of thedrill guide. The added leverage possible by the handle 18, allows forsignificantly improved drill guide assembly control. The handle member18 can be selectively positioned about the collar member 12, by rotatingthe clamp 24 to which the handle is fixed. The surgeon can thereforeeasily rotate the handle about the drill guide in order to find acomfortable position drilling while maintaining optimal visual contactbetween the tracker markers of the trackable member and the positionlocating cameras used to defined the position of the drill guide.

In an alternative embodiment, the trackable member can be selectivelypositioned about the collar member 12, by rotating the end cap 26 towhich the support rod 28 of the trackable member is fixed. A ratchettype mechanism in the end cap could provide fixed rotations of trackablemember, so that the surgeon can easily rotate the trackable member aboutthe axis drill guide in order to maintain optimal visual contact betweenthe tracker markers.

Radially extending guide tab 21 protrudes from the end flange 15 of theguide member 14. The tab 21 provides both a sight gauge marker withinthe depth sight slot 36 of the collar member 12, and additionallyprovides anti-rotation protection for the guide member within collarmember. The interior bore 44 defined by the radially inwardly projectingstop 42 is adapted to intimately receive the guide member such that thecollar member 12 can axially translate on the exterior surface of theguide member 14 with substantially concentric displacement. To ensurethis, a metal bushing 22 is additionally located within the collarmember 12 at the proximal end.

The first member abutting the workpiece and the second member abuttingthe drill bit in the drill chuck, depicted in the exemplary embodimentas the guide member 14 and the collar member 12 respectively, arepreferably generally elongated in shape and telescope within oneanother. However, the first and second members can be of any othershape, subject only to practicality and ease of use by the surgeon, andare required only to move relative to one another along a pathsubstantially similar to that of the drill bit. The two members do nothave to be engaged with each other, and could therefore be separated bya third intermediate member, providing relative motion exists betweenthe workpiece abutting member and the drill chuck abutting member.

In the preferred embodiment, the coiled compression spring 20 is locatedon the exterior of the drill guide assembly 10, and the member thatabuts the workpiece is the guide portion of the telescoping assemblywhile the drill chuck abutment member is the outer collar member, it ishowever to be understood that the present invention would be equallyfunctional with the collar member and guide member reversed or with thespring located within the assembly. Having the spring located on theexterior of the assembly, however, enables simplified cleaning. As such,the probability of bone debris or other material impeding compression ofthe spring, and therefore translation of the collar member on the guidemember, is minimal. This ensures smooth drill bit motion within theworkpiece. Additionally, the spring can be equivalently replaced by anyother extendingly biased member, such as a sprung scissor-typemechanism.

A percentage of the helical spring is always required to remainuncompressed. By locating the spring externally, the distal springreaction point flange 38 can be positioned at any point on the collarmember. This therefore permits the minimum uncompressed length of thespring to be taken up on the collar, rather than requiring the overalltool length to be extended by this amount if the spring was to belocated internally. Therefore, the exterior location of the springadditionally permits a shorter overall tool length, consequentlyimproving the facility of use by the surgeon.

Having an axially biased assembly according to the present invention,represents a considerably advantage over drill guide assemblies havingmembers that are radially, or frictionally, biased with one another. Insuch an assembly, the chuck abutting member does not automaticallyreturn to its fully extended position, but remains in the mostcompressed position. While this permits the hole depth sight to be readafter drilling the hole, it makes drilling a plurality of hole in quicksuccession impractical and more time consuming. The axially biasedspring system of the present invention, returns the drill guide to itsfully extended resting position after each hole drilled, and thereforepermits simplified multiple hole drilling, while the CAS systemaccurately measures the depth of each hole created.

The embodiments of the invention described above are intended to beexemplary only. The scope of the invention is therefore intended to belimited solely by the scope of the appended claims.

1. A method for defining the position and movement of a drill having abit portion engaged in a chuck, said method comprising: providing adrill guide adapted to receive the bit portion of the drill; fixing atrackable member comprising detectable element to a mobile portion ofsaid drill guide, said detectable element defining a unique position andorientation in three dimensional space of said trackable member andtherefore said drill guide; inserting the bit portion of the drill intosaid drill guide; positioning the bit portion over a workpiece surfaceand engaging said workpiece surface with a proximal end of one of thebit portion and said drill guide; and locating a position and trackingmovement of said trackable member fixed to said drill guide, and therebylocating the position and tracking the movement of the bit portion. 2.The method as defined in claim 1, further comprising the step ofcalibrating for a length of the bit portion of the drill.
 3. The methodas defined in claim 2, further comprising rapidly moving said mobileportion of said drill guide toward said workpiece surface, by depressingthe drill chuck abutting said drill guide, until a sudden stop when atip of the bit portion of the drill makes contact with said workpiecesurface, and detecting said sudden stop to define a zero position. 4.The method as defined in claim 1, further comprising using saidtrackable member to establish a distance traveled by said trackablemember.
 5. The method as defined in claim 4, further comprising usingsaid distance to calculate a depth of hole drilled by the bit portion ofthe drill.
 6. The method as defined in claim 1, further comprising thestep of using a computer assisted tracking system to locate the positionand track movement of said trackable member.
 7. The method as defined inclaim 6, wherein the step of locating the position and tracking movementof said trackable member is performed by an optical computer assistedtracking system.
 8. The method as defined in claim 1, further comprisingthe step of selectively rotating said trackable member about said mobileportion of said drill guide to maintain said trackable member indetectable contact with a sensor of a computer assisted surgery system.